Heat processing of fine-granular coal products



I HEAT-PROCESSING OF FINE-GRANULAR COAL PRODUCTS Filed Oct. 14, 1955HEAT PROCESSING OF FlNE-GRANULAR COAL PRODUCTS Alfred Jaeppelt,Dortmund, Otto Diettrich, Koln-Braunsfeld, and Othmar Werner,Koln-Bayenthal, Germany Application October 14, 1955, Serial No. 540,497Claims priority, application Germany October 14, 1954 13 Claims. (Cl.202-22) Our invention relates to the heat processing of finegranularfuel, such as coal dust for use in dust burning or gas producingequipment.

The heating of fine-granular, non-caking fuels in suspension within hotgases, as compared with the indirect heating of thin layers of coal, hasthe advantage of requiring less time due to the rapid heat transfer fromthe hot gases into the suspended coal granules. For instance, whendrying brown coal (German ligintic coal) a high continuous throughput isapplicable, even with a water content of the coal above 50%; and a heattreating period of less than one minute is suflicient.

Attempts have therefore been made to apply this method also for thepurpose of heating ncn-caking finegranular fuel to such highertemperatures as are required for carbonizing or coking the fuel. It hasbeen found, however, that under such conditions they rate of temperatureincrease is no longer as favorable as when heating the fuel to the lowerdrying temperatures at which a large temperture gradient is effectivebetween the heat-carrier gas and the solid coal granules. Anotherdisadvantage of thus carbonizing or coking the solid fuel in suspensionwithin a gas of the same flow direction is the fact that, on account ofthe high waste-gas temperature, the operation is economicallyunfavorable.

It is an object of our invention, therefore, to provide a continuousheat-processing method for the carbonization or coking of fine-granularfuel that affords basically the advantages of heating in gaseoussuspension but eliminates the above-mentioned disadvantages.

More particularly, it is an object of the invention to provide acontinuous heat processing of pulverulent coal products at carbonizingtemperature that is suitable to secure the large throughput required forindustrial application while also affording an improved heat economy andoverall efliciency as compared with the processes heretofore availablefor such purposes.

To this end, and in accordance with our invention, we heat the granularfuel in a sequence of heating steps that are consecutively graduatedfrom lower to higher temperatures respectively and that occur withinrespective heat exchangers of the cyclone type serially traversed by asingle, continuous flow of hot gases; and we introduce the fuelmaterial, suspended in the gas flow and conveyed thereby in the gas-flowdirection, into a heat exchanger near a point of the gas flow ofrelatively low temperature, and we then pass the fuel material,separated in the heat exchanger, back into the same gas flow but at apoint of higher temperature located, relative to the gas flow, ahead ofthe next-preceding heat exchanger, and so forth.

More specifically, we introduce the fuel material into the gas conduitthat connects the serially last cyclone with the cyclone next precedingin the gas path. After separation of the fuel material from the heatinggas in the last cyclone, we pass the fuel material through a sealing anddosagemetering device into the gas conduit leading into the nextpreceding cyclone, and coming from the gas outlet of thesecond-preceding cyclone. The

2,924,556 Patented Feb. 9, 1960 number of cyclones serially connected bygas conduits depends upon the desired degree of heating to be impartedto the fuel.

The fine-granular non-caking coal to be processed is to be introducedinto the above-described heating sequence in relatively dry condition.For the processing of fuel having a higher humidity content than desiredin the carbonizing process, and in accordance with another feature ofour invention, we first subject the granular fuel to drying orpreheating before introducing it into the main cyclone system. Thepre-heating is effected also by means of hot gases in which the granulesare suspended and conveyed in the flow direction of the gases,substantially in the konwn manner; but we join the preheating operationwith the main heating or carbonizing operation by employing acyclone-type heat exchanger in the pre-heating step and connecting thedust outlet of this cyclone directly with the inlet through which thefuel material is introduced into the main heating sequence.

When thus processing fuel material of high water content, it ispreferable to discharge the spent heating gases of the pre-heating ordrying operation separately from the flow of gases in the main heatingor carbonizing sequence. This prevents dilution of the tar-containinggas in the main heating sequence by the scavenging gases resulting fromthe pre-heating operation and containing an admixture of large amountsof steam. Besides, the waste gases of the main sequence are combustible,and hence can be utilized as fire gases in the required furnace or forother heating purposes.

The pre-heating operation and the main heating operation can be carriedout under nearly equal static pressures. It is preferable, however, toconduct the preheating operation under low or negative pressure, forinstance mm. water column, and the main heating under super-atmosphericpressure, for instance 400 mm. water column. The pressure loss in theheating operation is dependent upon the number of the cyclones, theamount of fuel throughout, and the temperature gradient of thescavenging or heating gases. The heating gases in the pre-heatingoperation may contain oxygen, whereas oxygen-free gas must be used inthe main heating or carbonizing operation. The pre-heating operationneed not be used when the fuel material to be processed is poor inwater.

The operations and flow of substances occurring in a process accordingto the invention are further apparent from the schematic diagram shownon the drawing.

A combustion furnace 1 is supplied with generator gas or blast-furnacetop gas at In, and with air at 1b. The gases of combustion are exhaustedby means of a blower 2 and pass from furnace 1 through a pipe 10 and apreheater pipe 3 into a cyclone 6 and thence through the top outlet ofthe cyclone and a pipe 6a into the blower 2. A small portion of thegases, used for preheating the fuel, is applied for regulating thepreheater-gas temperature by passing it through a pipe 2a back into thepreheater pipe 3. The temperature of the mixed gases at the entrance ofthe pre-heater pipe is thus kept between about 700 to 1100 C., dependingupon the water content of the fuel to be dried. The remaining majorportion of the preheater gases is discharged at 7 into the openatmosphere through a quantity-regulating member (not shown). The fuel tobe processed, for instance lignite (German brown coal) with a watercontent of about 50%, is supplied in granular form, preferably of agrain size below 10 mm, from a bin or hopper 4 through a rotating cellwheel 5 into the preheater pipe 3. The cell wheel 5 serves as a seal toprevent the escape of gas and it also controls the supply of granularfuel mass in accordance with the desired volumetric quantity.

The granules are entrained by the gas flow in pipe 3 and are conveyed insuspension to pass in the gas-flow direction toward the cyclone whilebeing dried by the hot gases entering through pipes and 2a. Afterdrying, the fuel may retain a water content of up to 4%, for in stance.In cyclone 6 the preheated and dried fuel material is separated bycentrifugal action at a temperature of 100 to 150 C., and is thensluiced out by means of a cell wheel 8.

Thence the fuel material enters through a pipe 8a directly into a gasconduit 10a of the main heater portion of the processing equipment andpasses sequentially through the cyclones 9, 10, 11 and 12. Each of thesecyclones is equipped with a gas sealing, dosage-metering and dischargingdevice designed, for instance, as a cell wheel 13, 14, and 16respectively. The heating gases required for the main heater portion,according to the schematic diagram, are produced as gases of combustionin a furnace 17. It is supplied at 17a with generator or top gas and at17b with air. The gases of combustion pass from furnace 17 sequentiallythrough a conduit 170 into cyclone 12, from the gas outlet of cyclone 12through a conduit 12a into cyclone 11, thence through a conduit 11a intocyclone 10, through another conduit 10a into cyclone 9, and through aconduit 18 into a condenser 19 from which the spent gases are dischargedat 19a.

The preheated fuel material, entering into the main heater portion ofthe system through pipe 8a, is entrained by the hot scavenging gaspassing through conduit 1% from cyclone 10 into cyclone 9. A direct heatexchange occurs in conduit 10a between the scavenging gas and the driedfine-granular fuel. This heat exchange is continued within the cyclone 9to a particularly effective degree. Thereafter, the fuel is dischargedthrough the cell wheel 13 and passes through discharge pipe 13a into gasconduit 11a. The hot gas passing from cyclone 11 through the conduit 11anow conveys the fuel into cyclone 10. In conduit 11a and, to a majordegree within cyclone 10, a second direct heat exchange at a highertemperature occurs between the hot gases and the fuel material. The fuelseparated in cyclone 10 then passes through dust discharge pipe 14a,while the scavenging gas passes through conduit 10a from the top outletof cyclone 1t) to cyclone 9.

In conduit 1211, the fine-granular fuel now admixes itself with thescavenging gas coming from cyclone 12 and is thus conveyed into cyclone11. In conduit 12a, and pmticularly in cyclone 11, the fuel is subjectedto another stage of heating treatment at a still higher temperatureSubsequently, the gas passes out of cyclone 11 through conduit 1111 intocyclone 10, while the heated fuel granules are discharged through cellwheel 15 and dust discharge pipe 15a. The discharged fuel, admixed withthe hot gases that pass from the combustion furnace 17 through conduit170, now is conveyed into cyclone 12. After the material is againheated, it is discharged at a temperature of 300 to 900 C. through cellwheel The above-mentioned final temperature of the fuel material dependsupon the properties of the fuel being treated, particularly upon thedesired residual content of volatile components. For instance, at afinal temperature of the processed fuel material of about 400 C., theresidual amount of volatile components may amount to 28 to 32% whenprocessing fine-granular brown coal (German lignite). The materialdischarging from pipe 16a can be cooled in the known manner if desired,for instance, by slaking with water.

The hot scavenging gas coming from the combustion furnace 17 at atemperature of 400m 1100 C., imparting its heat to the granular fuelmaterial sequentially in cyclones 12, 11, 10 and 9, becomes increasinglyladen with tar mist before it passes through conduit 18 at a temperatureof 150 to 300 C. into the condenser 19. The lower temperature limit of150 C. is applicable if a partial condensation of the tar mist isdesired prior to the exit gases entering into the condenser 19. Theupper temperature limit of 300 C." must not be exceeded forheat-economical reasons.

The gas conduit leading into the combustion furnace 17 at 17a and 17bare preferably each equipped with a blower, so that the combustible gasas well as the air of combustion are introduced in the furnace 17 andthus also into the heater portion of the plant under slightsuper-atmospheric pressure.

The cyclones 6, 9, 10, 11 and 12 are in accordance with the designsconventionally used for separating dust from air or gas; that is, theyoperate on the principle of centrifugal separation.

The hot scavenging gases required in the preheater and main heaterportions may also be produced in a single combustion furnace, since thetemperature of the gases entering into the preheater portion can becontrolled by the return of a cooler amount of these gases.

As a rule, the duration of the preheating or drying operation in thepreheater portion is about 20v to 60 seconds, and the fuel material maybe passed through the main heater portion within a period of 20 secondsto 2 minutes, for instance.

The heat-processed fuel material obtained in the abovedescribed mannercan be used, for instance, for the operation of coal-dust burners or forthe purpose of gas production. The process is particularly advantageousin permitting a high throughput at a particularly favorable heateconomy.

In order to prevent the condensation of tar mists in the main heatingportion and the precipitation of tar onto the coal granules, and alsofor obtaining a largest possible yield in tar, the exit gas temperatureof the main heating portion is to be kept above the dew point of the tarwithin the gas. This is done by suitably controlling the temperature orquantity or both magnitudes of the gas supply. The danger that tar mistsmay con-. dense onto the coal to be heated is very slight when thepreheating step is combined with the main heating sequence, that is whenthe process is applied to the heating of fuels of high water contents.This is so because the fine-granular fuel is directly sluiced from thepreheater portion into the main heater portion so that no appreciableheat losses are involved. However, if it is desired to obtain a tar ofgreatest possible degree of cracking, for instance when carbonizingfuels whose tar is of inferior. quality, then it may be favorabletooperate so that the exit temperature of the scavenging gases leaving themain heating portion is below the dew point of the tar vapors in orderto cause a condensation of the heavy components or the precipitation ofthese components onto the preheated coal. The tar thus condensed andprecipitated is then re-distilled in the main heating portion.

The heat processing method, according to the inven-.

tion, is particularly advantageous for the coking of mixtures composedof non-caking and caking fuels, such as non-caking and caking bituminouscoal. The non-caking componentof such mixtures may consist oflow-volatile or high-volatile bituminous coal such as German Steinkohleof the non-caking variety, lignite such as brown coal of German origin,or peat. The caking component may consist of low-volatile orhigh-volatile bituminous coal such as German Steinkohle? of the leanvariety. For the production of a good mixed coke from such materials, itis necessary to mix the non-baking fuel in deg asified condition withthe baking fuel prior to coking the mixture. It is preferable to adaptthe non-caking coal to this use by aspecific or predetermined degree ofdegasification, this being dependent upon the caking qualities of thecaking coal to be admixed. Such an adaptation of the gas contents of thenon-baking coal is possible in a particularly simple manner by applyingthe heating method according. to the invention. For

instance, it has been found. particularly advantageous if the heating ofnon-caking fuel. material in the main heater portion is so carried outthat'a residual content of volatile components in an amount of 20 to 25%is obtained. When the resulting material is mixed in a proportion of 1:1with a good caking coal having a content of dry volatile matter of about30% for instance,

the mixture, upon coking in a coke furnace, produces a metallurgicalcoke of good quality; that is, a coke .material suitable for thesmelting of iron ore in blast furnaces.

We claim:

1. The method of carbonizing non-caking fine-granular coal in suspensionwithin heating gases and in continuous operation, which comprises thesteps of passing a flow of hot substantially oxygen-free combustiongases serially through a number of cyclones so that said cyclones havedecreasing temperatures respectively from the serially first to the lastcyclone, charging dry granular coal into the hot combustion gas flowentering the last cyclone whereby the coal is heated and separated fromthe gas in said last cyclone, passing the coal separated from the gasand still in heated condition from each cyclone, excepting the firstone, into the hot combustion gas flow entering the next precedingcyclone, the gas being hotter than the coal, whereby the coal is heatedto a higher temperature and again separated from the gas flow, adjustingthe volumetric quantity of the gas flow entering the first cyclone asrequired to maintain the exit temperature of the tar-laden gases at thelast cyclone above the dew point of the tar vapors entering into the gasdue to carbonization of the coal, and discharging the carbonized coalfrom the first cyclone of the gas-flow series, the coal being carried insuspension co-currently by the hot combustion gases flowing to thecyclones.

2. The method of heating coal comprising suspending the coal in finegranular form in a current of hot gases, passing the coal and gasesco-currently through a zone in which the gas pre-heats the suspendedcoal and thence co-currently into a cyclone separator in which furtherheat exchange between the gases and the coal takes place, removing thecoal separated from the gas in the said separator and passing theseparated coal in co-current suspension in a current of gases hotterthan the first into a second cyclone separator in which the coal isheated to a higher temperature than in the first cyclone separator.

3. The method of drying and heating coal comprising suspending the coalin fine granular form in a current of hot gases, passing the coal andgases co-currently upwardly through an elongated zone in which the gaspreheats the suspended coal and thence co-currently into a cyclonicseparation zone in which further heat exchange between the gases and thecoal takes place to dry the latter, removing the coal separated from thegas in the said separation zone and passing the separated coal inco-current suspension in a current of gases hotter than in the firstcyclonic zone and hotter than said separated coal, into a secondcyclonic separation zone in which the coal is heated to a highertemperature than in the first cyclonic separation.

4. The method of carbonizing coal comprising suspending the coal in finegranular form in a current of hot gases, passing the coal and gasesco-currently through a zone in which the gas pre-heats the suspendedcoal and thence co-currently into a cyclone separator in which furtherheat exchange between the gases and the coal 'takes place, removing thecoal separated from the gas in the said separator and passing theseparated coal in co-current suspension in a current of oxygen-freecombustion gases hotter than the first gases into a second cycloneseparator in which the coal is heated to a higher temperature than inthe first cyclone separator.

5. A continuous process for heating fine granular noncaking coal insuspension in hot gas in at least three stages .6 including a cyclonicheating and separation in each stage, the coal being progressivelyheated up from the first to the third" stage, comprising passing thegranular coal in a stream of hot gas to' a third stage cyclonic heat- 1granular coal into said hot gases and passing these gases and coal intothe first stage cyclonic heating and separation.

6. The process of claim 5 in which the said heating is at a temperaturesufiiciently high to at least partially carbonize the coal.

7. The process of claim 5 in which the hot gases are combustion gasessubstantially free of oxygen and are at carbonizing temperature in atleast the third stage cyclonic heating.

8. The method of carbonizing non-caking fine-granular coal in suspensionwithin heating gases and in continuous operation in several heating-upstages, which comprises the steps of passing a flow of hot combustiongases serially through a plurality of cyclonic coal heating-up zones atan exit temperature between about C. and about 300 C. at the lastcyclonic zone, charging dry granular non-caking coal into the gasflowing into the serially last cyclonic zone, passing the cyclone-heatedcoal, separated from the cyclone separated gas, from each cyclonic zone,excepting the first one, into the gas flow entering the next precedingcyclonic zone, which entering gas is hotter than the coal, anddischarging the carbonized coal from the first cyclonic zone of thegas-flow series, the coal being carried in suspension co-currently bythe hot combustion gases flowing to the cyclonic zones.

9. The method of carbonizing non-caking fine-granular coal in suspensionwithin heating gases and in continuous operation in several heating-upstages, which comprises the steps of pre-heating moist granular coal ingaseous suspension and separating the dry coal from the moisture-ladengas, passing a flow of hot combustion gases substantially oxygen-freeserially through a plurality of cyclonic coal heating-up zones at anexit temperature between about 150 C. and about 300 C. at the lastcyclonic zone, charging the pre-heated coal when still in heatedcondition into the gas flow entering the serially last cyclonic zonehaving the lowest temperature of said plurality of cyclonic zones,passing the cycloneheated coal, separated from the cyclone separatedgas, from each cyclonic zone, excepting the first one, into the gas flowentering the next preceding cyclonic zone, having a higher temperature,and discharging the carbonized coal from the first cyclonic zone of thegas-flow series, the coal being carried in suspension co-currently bythe hot combustion gases flowing to the cyclones.

10. The method of making coke material suitable for smelting iron ore inblast furnaces, comprising carbonizing non-caking fine-granular coal insuspension within heating gases and a continuous operation in severalheating-up stages, by the steps of passing a flow of hot combustiongases serially through a plurality of cyclonic coal heating-up zones atan exit temperature between about 150 C. and about 300 C. at the lastcyclonic zone, charging dry granular coal into the gas flowing into theserially last cyclonic zone, passing the cyclone-heated coal, separatedfrom the cyclone separated gas, from each cyclonic zone, excepting thefirst one, into the gas flow entering the next preceding cyclonic zone,which entering gas is hotter than the coal, and discharging thecarbonized coal from the first cyclonic zone of the gas-flow series,

said heating .being carried out so that a carbonized prodv not having aresidual content of volatile components of about 20 to 25% results, andmixing the product with a good caking coal and coking the mixture.

11. The method of removing volatiles from coal by direct contact withhot gases, comprising suspending the coal in fine granular form in acurrent of hot carrier gases, passing the coal and gases cocurrentlythrough a zone in which the gas directly pre-heats the suspended coaland thence co-currently into a cyclone separator in which further directheat exchange between the gases and the coal takes place, removing thecoal separated from the gas in the said separator and passing theseparated coal in co-current suspension, in a current of gases hotterthan the first and which entering gas is hotter than the coal, into asecond cyclone separator in which the coal is directly heated by saidhotter gases to a higher temperature than in the first cycloneseparator.

12. A continuous process for carbonizing fine granular non-caking coalin suspension in hot non-oxidizing combustion gas in at least threestages including a cyclonic heating and separation in each stage, thecoal being progressively heated up from the first to the third stage bythe hotter entrant gases to each stage, comprising passing the granularcoal in a stream ofsaid hot gas to the third stage cyclonic heating andseparation, removing the hot gases separated from the third stage,removing granular coal separated in the first stage cyclonic heating andseparation and conveying it in the hot gases separated from the thirdcyclone stage into a second stage cyclonic heating and separation,removing the granular coal separated in the second cyclonic stage andpassing it in said first-mentioned stream of hot gases to the thirdstage cyclonic heating and separation as aforesaid, removing the hotgases separated from the second cyclonic heating stage and introducinggranular coal into said hot gases, the entrant gases being hotter thanthe coal, and passing these gases and coal into the first stage cyclonicheating and separation, the exit gases from the first stage heatingbeing at about 150 to 300 C., the inlet gases to the third stage heatingbeing at about 400 to 1100 C.

13. A continuous process for carbonizing fine granular pre-heated and atleast partly dried non-caking coal in suspension in hot non-oxidizingcombustion gas in at least three stages including a cyclonic heating andseparation in each stage, the coal being progressively heated up fromthe first to the third stage, comprising passing the granular coal'in astream of said hot gas to the third stage cyclonic heating andseparation, removing the hot gases separated from the third stage,removing granular coal separated in the first stage cyclonic heating andseparation and conveying it in the hot gases separated from the thirdcyclone stage into a second stage cyclonic heating and separation,removing the granular coal separated in the second cyclonic stage andpassing it in said firstmentioned stream of hot gases to the third stagecyclonic heating and separation as aforesaid, removing the hot gasesseparated from the second cyclonic stage and introducing pre-heated andpartly dried granular coal into said hot gases and passing these gasesand the coal into the first stage cyclonic heating and separation, theexit gases from the first stage heating being at about to 300 C., theinlet gases to the third stage heating being at about 400 to 1100 C.,the pre-heating of the coal being carried out by suspending the granularcoal in hot gases and causing the suspension to whirl about in acyclonic zone, separating the coal from the gas in said zone andintroducing said coal into the first stage cyclonic heating andseparation, as recited.

References Cited in the file of this patent UNITED STATES PATENTS Re.17,181 McEwen Ian. 1, 1929 2,085,903 Fitz July 6, 1937 2,512,076 SinghJune 20, 1950 2,534,051 Nelson Dec. 12, 1950 2,623,011 Wells Dec. 23,1952 2,654,699 Lesher Oct. 6, 1953 2,706,706 Pettyjohn Apr. 14, 19552,719,112 Kearby et al. Sept. 27, 1955 2,734,853 Smith et al Feb. 14,1956 2,735,804 Boston et al. Feb. 21, 1956 2,751,334 Scott June 19, 1956FOREIGN PATENTS 670,882 Germany Jan. 27, 1939 501,374 Great Britain Feb.27, 1939 OTHER REFERENCES Sohns et al.: Industrial and EngineeringChemistry, page 461, March 1955.

1. THE METHOD OF CARBONIZING NON-CAKING FINE-GRANULAR COAL IN SUSPENSIONWITHIN HEATING GASES AND IN CONTINUOUS OPERATION, WHICH COMPRISES THESTEPS OF PASSING A FLOW OF HOT SUBSTANTIALLY OXYGEN-FREE COMBUSTIONGASES SERIALLY THROUGH A NUMBER OF CYCLONES SO THEAT SAID CYCLONES HAVEDECREASING TEMPERATURES RESPECTIVELY FROM THE SERIALLY FIRST TO THE LASTCYCLONE, CHARGING DRY GRANULAR COAL INTO THE HOT COMBUSTION GAS FLOWENTERING THE LAST CYCLONE WHEREBY THE COAL IS HEATED AND SEPARATED FROMTHE GAS IN SAID LAST CYCLONE, PASSING THE COAL SEPARATED FROM THE GASAND STILL IN HEATED CONDITION FROM EACH CYCLONE, EXCEPTING THE FIRSTONE, INTO THE HOT COMBUSTION GAS FLOW ENTERING THE NEXT PRECEDINGCYCLONE, THE GAS BEING HOTTER THAN THE COAL, WHEREBY THE COAL IS HEATEDTO A HIGHER TEMPERATURE AND AGAIN SEPARATED FROM THE GAS FLOW, ADJUSTINGTHE VOLUMETRIC QUANTITY OF THE GAS FLOW ENTERING THE FIRST CYCLONE ASREQURED TO MAINTAIN THE EXIT TEMPERATURE OF THE TAR LADEN GASES AT THELAST CYCLONE ABOVE THE DEW POINT OF THE TAR VAPORS ENTERING INTO THE GASDUE TO CARBONIZATION OF THE COAL, AND DISCHARGING THE CARBONIZED COALFROM THE FIRST CYCLONE OF THE GAS-FLOW SERIES, THE COAL BEING CARRIED INSUSPENSION CO-CURRENTLY BY THE HOT COMBUSTION GASES FLOWING TO THECYCLONES.